1. Field of the Invention
The present invention relates to an image display apparatus, a driving circuit for the image display apparatus, and an image display method.
2. Description of the Related Art
In recent years, large flat-screen display apparatuses have extensively been studied and developed. The present inventors have studied a large flat-screen display apparatus using a cold cathode device as an electron source.
Conventionally, two types of devices, namely hot and cold cathode devices, are known as electron-emitting devices. Known examples of cold cathode devices are surface-conduction type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of surface-conduction type electron-emitting devices is described in, e.g., M. I. Elinson, “Radio Eng. Electron Phys., 10, 1290-(1965) and other examples will be described later.
A surface-conduction type electron-emitting device utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by causing a current to flow parallel through the film surface. Surface-conduction-conduction type electron-emitting devices include electron-emitting devices using an Au thin film [G. Dittmer, “Thin Solid Films”, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)], a carbon thin film [Hisashi Araki et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 22 is a plan view showing the device by M. Hartwell et al, described above as a typical example of the device structures of surface-conduction type electron-emitting devices. Referring to FIG. 22, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown having FIG. 22. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 22 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown having a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction type electron-emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In the forming processing, for example, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the two ends of the conductive thin film 3004 so as to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the forming processing, electrons are emitted near the fissure.
Known examples of FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “Physical properties of thin film field emission cathodes with molybdenium cones”, J. Appl. Phys., 47, 5248 (1976).
FIG. 23 is a sectional view showing the device by C. A. Spindt et al, described above as a typical example of an FE type device structure. Referring to FIG. 23, reference numeral 3010 denotes a substrate; numeral 3011 denotes emitter wiring made of a conductive material; numeral 3012 denotes an emitter cone; numeral 3013 denotes an insulating layer; and numeral 3014 denotes a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and the gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012. As another FE type device structure, there is an example in which an emitter and a gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 23.
A known example of MIM type electron-emitting devices is described in C. A. Mead, “Operation of Tunnel-Emission Devices”, J. Appl. Phys., 32,646 (1961). FIG. 24 shows a typical example of the MIM type device structure. FIG. 24 is a sectional view of the MIM type electron-emitting device. Referring to FIG. 24, reference numeral 3020 denotes a substrate; numeral 3021 denotes a lower electrode made of a metal; numeral 3022 denotes a thin insulating layer having a thickness of about 100 A; and numeral 3023 denotes an upper electrode made of a metal and having a thickness of about 80 to 300 A. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper electrode 3023 and the lower electrode 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above described cold cathode devices can emit electrons at a temperature lower than that for hot cathode devices, they do not require any heater. The cold cathode device therefore has a structure that is more simple than that of the hot cathode device and can be micropatterned. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the hot cathode device is low because it operates upon heating by a heater. For this reason, applications of cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the above surface-conduction type electron-emitting devices are advantageous because they have a simple structure and can be easily manufactured. For this reason many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of surface-conduction type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, electron sources, and the like have been studied.
As an application to image display apparatuses, in particular, as disclosed in U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using the combination of a surface-conduction type electron-emitting device and a fluorescent substance which emits light upon reception of electrons has been studied. An image display apparatus using the combination of a surface-conduction type electron-emitting device and a fluorescent substance is expected to have improved characteristics over other conventional image display apparatuses. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require a backlight, because it is of a self-emission type apparatus, and it has a wide viewing angle.
A method of driving a plurality of FE type electron-emitting devices arranged side-by-side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the present applicant. A known example of an application of FE type electron-emitting devices to an image display apparatus is a flat display apparatus reported by R. Meyer et al. [R. Meyer: “Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)].
An example of an application of a larger number of MIM type electron-emitting devices arranged side-by-side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present applicant.
The present inventors have examined cold cathode devices using various materials, methods, and structures in addition to those described above. The present inventors have further studied a multi-electron-source formed by laying out many cold cathode devices, and an image display apparatus using this multi-electron-source.
The present inventors have devised a multi-electron-source using an electrical wiring method shown in, e.g., FIG. 25. That is, the multi-electron-source is formed by two-dimensionally laying out many cold cathode devices in a matrix, as shown in FIG. 25.
Referring to FIG. 25, reference numerals 4001 denote cold cathode devices; numerals 4002 denote row-direction wirings; and numerals 4003 denote column-direction wirings. In practice, the row- and column-direction wirings 4002 and 4003 have finite electrical resistances, which are indicated by resistors 4004 and 4005 in FIG. 25 of the wires. This wiring method is called a simple matrix wiring method. FIG. 25 shows a 6×6 matrix for the sake of illustrative convenience, but the matrix scale is limited to this. For example, in a multi-electron-source for an image display apparatus, devices necessary for desired image display are laid out and wired.
In the multi-electron-source formed by laying out cold cathode devices in a simple matrix, proper electrical signals are applied to the row- and column-direction wirings 4002 and 4003 in order to output desired electrons. For example, to drive cold cathode devices on an arbitrary row within the matrix, a selection voltage Vs is applied to row-direction wiring 4002 on the selected row, while a non-selection voltage Vns is applied to row-direction wirings 4002 on unselected rows. In synchronism with this, a driving voltage Ve for outputting electrons is applied to the column-direction wirings 4003. According to this method, if a voltage drop caused by the resistors 4004 and 4005 is ignored, a voltage (Ve−Vs) is applied to cold cathode devices on a selected row, and a voltage (Ve−Vns) is applied to cold cathode devices on unselected rows. If the voltages Ve, Vs, and Vns are set to proper magnitude values, electrons would be output at a desired strength from only cold cathode devices on the selected row. If different driving voltages Ve are applied to respective column-direction wirings, electrons would be output at different strengths from respective devices on the selected row. If the application time of the driving voltage Ve is changed, the electron output time would be changed. A voltage (Ve−Vs) to be applied to a selected device will be referred to as Vf. According to another method of obtaining electrons from the multi-electron-source having a simple matrix layout, the multi-electron-source is driven by connecting a current source for supplying a current necessary for outputting desired electrons, instead of a voltage source for applying the driving voltage Ve to the column-direction wiring. The current flowing through the current source will be referred to as a device current If, and the amount of emitted electrons will be referred to as an emission current Ie.
The multi-electron-source formed by laying out cold cathode devices in a simple matrix can be variously applied and suitably used as an electron source for an image display apparatus by properly applying an electrical signal corresponding to, e.g., image information.
In U.S. Pat. No. 5,734,361, driving of electron-emitting devices laid out in a matrix is described. Particularly, correction of the driving signal is also described.